全文获取类型
收费全文 | 4068篇 |
免费 | 173篇 |
国内免费 | 27篇 |
专业分类
化学 | 2933篇 |
晶体学 | 12篇 |
力学 | 106篇 |
数学 | 574篇 |
物理学 | 643篇 |
出版年
2023年 | 34篇 |
2022年 | 96篇 |
2021年 | 97篇 |
2020年 | 93篇 |
2019年 | 93篇 |
2018年 | 63篇 |
2017年 | 48篇 |
2016年 | 130篇 |
2015年 | 100篇 |
2014年 | 146篇 |
2013年 | 240篇 |
2012年 | 289篇 |
2011年 | 305篇 |
2010年 | 184篇 |
2009年 | 186篇 |
2008年 | 294篇 |
2007年 | 269篇 |
2006年 | 211篇 |
2005年 | 234篇 |
2004年 | 201篇 |
2003年 | 147篇 |
2002年 | 148篇 |
2001年 | 53篇 |
2000年 | 40篇 |
1999年 | 27篇 |
1998年 | 33篇 |
1997年 | 31篇 |
1996年 | 44篇 |
1995年 | 34篇 |
1994年 | 29篇 |
1993年 | 20篇 |
1992年 | 23篇 |
1991年 | 25篇 |
1990年 | 36篇 |
1989年 | 21篇 |
1988年 | 26篇 |
1987年 | 16篇 |
1986年 | 14篇 |
1985年 | 26篇 |
1984年 | 15篇 |
1982年 | 18篇 |
1981年 | 15篇 |
1980年 | 12篇 |
1979年 | 12篇 |
1978年 | 13篇 |
1977年 | 11篇 |
1976年 | 5篇 |
1975年 | 5篇 |
1974年 | 6篇 |
1973年 | 8篇 |
排序方式: 共有4268条查询结果,搜索用时 31 毫秒
11.
12.
Eleonora Catsigeras Jean-Marc Gambaudo Fernando Moreira 《Proceedings of the American Mathematical Society》1998,126(1):297-304
We show that, among area contracting embeddings of the 2-disk, infinitely renormalizable maps with a bounded geometry either have positive topological entropy or correspond to a cascade of period doubling.
13.
In this paper we address a two-dimensional (2D) orthogonal packing problem, where a fixed set of small rectangles has to be placed on a larger stock rectangle in such a way that the amount of trim loss is minimized. The algorithm we propose hybridizes a placement procedure with a genetic algorithm based on random keys. The approach is tested on a set of instances taken from the literature and compared with other approaches. The computation results validate the quality of the solutions and the effectiveness of the proposed algorithm. 相似文献
14.
Julio Penin Santos Fernando J.G. Landgraf Geraldo Caixeta Guimarães 《Journal of magnetism and magnetic materials》2006
The paper describes effect of texture on the anisotropy of magnetic properties and shows that an Epstein strip arrangement including strips cut in a direction 45° to the rolling direction gives property values that are closer to the average values than the traditional RD+TD arrangement. 相似文献
15.
Marcos F. de Campos Marília Emura Fernando J.G. Landgraf 《Journal of magnetism and magnetic materials》2006
Electrical steels, when submitted to operation, present continuous decrease of their magnetic properties, depending on the carbon content. This effect is attributed to the increase of the size of carbides, a process also known as coarsening or Ostwald Ripening. Loss separation can offer a better understanding of this phenomenon. Experimental results show that all effect of aging is inside the hysteresis loss component, with the excess losses unaffected. The carbon content in electrical steels should be less than 25 ppm to avoid magnetic aging. 相似文献
16.
Fernando Torres 《Semigroup Forum》1997,55(3):364-379
This work was realized while the author was ICTP (Trieste - Italy) with a grant from the International Atomic Energy Agency
and UNESCO. 相似文献
17.
The absorption of pulsed CO2-laser radiation by ethylene has been measured at total pressures from 25 to 3000 Torr, using the P(12) and P(14) lines in the 10.6 m band, with incident fluences from 0.1 to 0.7 J/cm2. Marked deviations from the Beer-Lambert absorption law were observed, with the effective absorption coefficient varying with pressure, fluence, absorption path-length and the addition of non-absorbing gas. Pressure broadening of the rotational lines of the ethylene absorption spectrum was shown to be the major cause of these deviations, together with lesser effects which can be attributed to the rise in temperature of the absorbing gas during the laser pulse. 相似文献
18.
A novel experimental procedure to obtain α-benzyl-β-keto esters from the Heck reaction between arenediazonium tetrafluoroborate salts and Baylis-Hillman (BH) adducts in the presence of Pd(OAc)2 as catalyst is described. The methodology is simple, straightforward and the use of arenediazonium salts as opposed to conventional arylhalides/triflates over the usual Heck reaction is highlighted. 相似文献
19.
Alessandro Boido Francesco Savelli Fernando Sancassan 《Journal of heterocyclic chemistry》1997,34(5):1643-1644
Following a previous experiment, an original heteropolycyclic structure 4 was obtained by a reaction of chloroacetyl chloride with compound 3 bearing a conjugated double bond system. The condensation develops with an initial NH-chloroacetylation and ring closure by quaternarization of the pyridine nitrogen. This is achieved through an 1,4 -cycloaddition of chloroketene to make a pyranone ring. 相似文献
20.